Deactivation of Ti and Zr half-metallocene complexes activated with B(C6F5)3: a case study in constructing DFT-based QSARs to predict unimolecular rate constants

Abstract

Two deactivation pathways of Ti and Zr half-metallocene complexes activated with B(C₆F₅)₃ in toluene solvent were studied using Density Functional Theory (DFT) with dispersion corrections: (a) H transfer from the counterion to Me initiating group to release methane and (b) C₆F₅ transfer from the counterion to the metal. Transition state geometries and energies were computed for twenty-seven complexes, and the barrier height for the C₆F₅ transfer pathway was linearly correlated to the amount of steric congestion near the metal. Unimolecular rate constants for catalyst deactivation were predicted for all 27 catalysts by constructing a DFT-based quantitative structure activity relationship (QSAR). This QSAR was constructed by using the DFT-computed energy barrier (ΔV₀) and vibrational frequency along the reaction coordinate (ν^‡) as chemical descriptors and fitting QSAR parameters to experimental data for reference systems. The computed rate constants were in excellent agreement with the available experimental data. Specifically, the dominant deactivation pathway for each catalyst and the relative deactivation rates of different catalysts were correctly predicted. Of note, the IndTi(OC₆H-2,3,5,6-Ph₄)Me₂/B(C₆F₅)₃ system is predicted to have a good combination of slow deactivation and high olefin polymerization rates.